There is a need for a class of vessels that can counter enemy mines, submarines and fast attack craft in littoral waters. Such a vessel is being proposed by the U.S. Navy as the Littoral Combat Ship (LCS). The LCS is to be a small, fast, surface combatant that would use modular “plug-and-fight” mission payload packages, including unmanned vessels. The LCS must also be able to perform a host of secondary missions such as intelligence gathering, surveillance, reconnaissance, maritime intercept, special operations support, logistics support, mine clearing and homeland defense. The LCS acts as a host vessel to accomplish secondary missions performed through the use of manned or unmanned off-board vessels. For example, it is envisioned that the following types of off-board vessels may be used: rigid hull inflatable boats (RHIB), unmanned underwater vehicles (UUV), and unmanned surface vehicles (USV). These off-board vessels could simultaneously be performing such duties as mine clearing, reconnaissance and delivering special operations forces to shore. In order for a host vessel to perform these secondary missions, it would be preferable to provide a system that could quickly and efficiently perform launch and recovery activities of multiple types of off-board vessels. In addition, launch and recovery by the host vessel of such vessels must be possible day or night and in a variety of sea conditions.
Safety is a key concern during launch and recovery activities. In rough seas the recovery is further hampered by the vertical change or heave of the respective vessels due to waves. The launch and recovery must be done in such a fashion so as to avoid damage to the off-board vessel as well as the host ship. The act of bringing a smaller vessel on board a larger vessel obviously requires contact. However, colliding with the host vessel or the recovery apparatus, such as a winch, crane cables, or tethers, can damage surface and underwater vehicles.
One recovery technique is disclosed in Apparatus and Method for Deploying, Recovering, Servicing and Operating an Autonomous Underwater Vehicle (AUV), U.S. Pat. No. 6,390,012, wherein a tether is lowered under the host vessel from which a “latch” vehicle is deployed. The “latch” vehicle is remotely piloted to the AUV and then reconnected to the tether. The entire process occurs underwater so as to avoid the problem of heave, however, the system does not lend itself to recovery while the host vessel is moving. Moreover, the remote control aspect of the “latch” vehicle adds an extra layer of complexity.
One of the greatest dangers involved in the launch or recovery is discovery by an enemy while the LCS is vulnerable. As provided earlier, the LCS type vessel depends on speed for survivability. Therefore, the launch and recovery of an off-board vessel is preferably arranged while the host vessel is underway. One method of recovery involves driving the smaller vessel onto a ramp at the back of the ship. The ship can either be stationary or moving at a slower speed than the off-board vessel. This method requires a specially designed ship's architecture for the ramp and ample storage space. The smaller vessel must also have sufficient power to propel itself from the water onto the inclined ramp. In addition, a crane must also be included to lift the off-board vessel off of the ramp if more than one recovery is performed.
The alternative to the ramp is simply a deployed lifting device, which requires close contact between the two vessels. The launch and recovery is typically performed by a boom or crane attachment. For example, Launch and Recovery System for Unmanned Underwater vehicles, U.S. Pat. No. 6,779,475, describes a host vessel with stem end wall that converts to a ramp coupled with a boom that includes a capture mechanism. In this embodiment, the UUV must be directed to the surface within the reach of the boom while the host vessel is motionless. The UUV is directed by a homing signal on the boom for capture. Other lifting devices, such as Boat-Lift Systems and Methods, U.S. Pat. No. 6,782,842 also describes a lifting device mounted at the stem of a larger vessel. The smaller vessel must be directed to the stem for attachment. In both examples, capture and recovery is difficult in a heavy sea and impossible while the larger vessel is underway. In addition, a diver is sometimes required to assist in the connection or release of the off-board vessel.
In combat situations, speed and flexibility of the recovery system is paramount for completion of a successful mission. The examples illustrated require calm seas, divers to perform the connection between the lift and off-board vessel and good visibility. In littoral waters, secrecy and speed require the ability to launch and recover while the host vessel is moving. Furthermore, special operations and reconnaissance launches typically occur at night and in rough seas.
Therefore, there is a need for a launch and recovery system that can be performed while the ship is at speed. It is also preferable to avoid the use of divers in order to limit injury and the complexity of collecting and recovering both divers and the smaller vessel. Obviously, space is at a premium aboard a combat ship. There is also a need to minimize the size of the launch and recovery system aboard a ship. Accordingly, there is a need for a launch and recovery system that enhances the survivability of the host vessel, utilizes a minimum of deck space, and allows for the recovery of off-board vessels with a minimum of complexity.